Galaxy protoclusters at the cosmic noon host a large population of massive, often dusty, and starbursty or star-forming galaxies. However, this picture radically changes by z=1, when red ellipticals dominate the cores of massive clusters. The transition between these two states must be mediated by some environmentally driven mechanism that quenches the star formation and morphologically transform these galaxies in a short period of time. Gravitational interactions are expected to be frequent during protocluster assembly and could be responsible for both stimulating star formation (via wet mergers) as well as for shutting it down in short timescales by triggering AGN activity due to the loss of angular momentum and channeling of gas towards the central supermassive black hole (SMBH). We aim to identify hidden type-2 AGN within a sample of massive HAEs in two evolutionary distinct protoclusters at 2<z<3. Together with previous NIR (Hα/[NII] ratios) and (sub-)millimeter (gas mass) campaigns, we will determine the interplay between star-formation and AGN activity during the assembling process of protoclusters, reveal their true AGN fractions, and investigate the environmentally accelerated evolution of massive star-forming galaxies into passive ellipticals therein.
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